Method for fabricating multilayer environmental barrier coatings

ABSTRACT

A method of making a multilayer environmental barrier coating for a ceramic matrix composite is provided, comprising the steps of: plasma spray coating an oxide-based bond coat over top of the ceramic matrix composite and depositing a columnar top coat over the oxide-based bond coat.

RELATED APPLICATIONS

This application is related to and claims priority to U.S. ProvisionalPatent Application Ser. No. 61/777,054, filed on Mar. 12, 2013 entitled“Method for Fabricating Multi-Layer Environmental Barrier Coatings.” Thesubject matter disclosed in that provisional application is herebyexpressly incorporated into the present application in its entirety.

TECHNICAL FIELD AND SUMMARY

This present disclosure relates to methods of fabricating multilayerenvironmental barrier coatings for substrates such as ceramic matrixcomposites, and in particular, to methods of fabrication that includethe combination of plasma spraying and either electron beam physicalvapor deposition or directed vapor deposition.

An illustrative embodiment of the present disclosure includes a methodof making a multilayer environmental barrier coating for a ceramicmatrix composite, comprising the steps of: plasma spray coating anoxide-based bond coat over top of the ceramic matrix composite;selecting a method of applying a columnar top coat over the oxide-basedbond coat, wherein the method of applying the columnar top coat isselected from the group consisting of electron beam physical vapordeposition and directed vapor deposition; and depositing a columnar topcoat over the oxide-based bond coat according to the selected method ofapplying the columnar top coat.

In the above and other embodiments, the method of making the multilayer,environmental barrier coating may further include: selecting the methodof applying the columnar top coat, being decided by evaluating thebenefits and detriments of either the electron beam physical vapordeposition and the directed vapor deposition methods and how thosebenefits and detriments affect the columnar top coat when sprayed on theoxide-based bond coat; the oxide-based bond coat is selected from thegroup consisting of mullite, mullite+Si, HfSiO₄+SiO₂+Si,HfSiO₄+SiO₂+Al₂O₃+Si, RE₂Si₂O₇+Al₂O₃+Si, RE₂Si₂O₇+Al₂O₃+SiO₂+Si, andSiO₂+Al₂O₃+Si, (wherein RE is selected from the group consisting of atleast one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium,terbium, gadolinium, europium, samarium, promethium, neodymium,praseodymium, cerium, lanthanum, yttrium, and scandium), the columnartop coat is selected from the group consisting of RE₂Si₂O₇ and RE₂SiO₅(wherein RE is selected from the group consisting of at least one oflutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium,gadolinium, europium, samarium, promethium, neodymium, praseodymium,cerium, lanthanum, yttrium, and scandium), RE₂O₃-stabilized ZrO₂(wherein RE is selected from the group consisting of at least one oflutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium,gadolinium, europium, samarium, promethium, neodymium, praseodymium,cerium, lanthanum, yttrium, and scandium), and RE₂O₃-stabilized HfO₂(wherein RE is selected from the group consisting of at least one oflutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium,gadolinium, europium, samarium, promethium, neodymium, praseodymium,cerium, lanthanum, yttrium, and scandium); the oxide-based bond coatbeing the mullite+Si, wherein the Si is present in an amount betweenabout 10 wt % and about 40 wt %, with the balance being mullite; theoxide-based bond coat being the HfSiO₄+SiO₂+Si, wherein the Si ispresent in an amount between about 10 wt % and about 40 wt %, the SiO₂is present in an amount between about 10 wt % and about 30 wt %, and thebalance being HfSiO₄; the oxide-based bond coat being theHfSiO₄+SiO₂+Al₂O₃+Si, wherein the Si is present in an amount betweenabout 10 wt % and about 40 wt %, the SiO₂ is present in an amountbetween about 10 wt % and about 30 wt %, the Al₂O₃ is present in anamount between about 0.1 wt % and about 10 wt %, and the balance beingHfSiO₄; the oxide-based bond coat being the RE₂Si₂O₇+Al₂O₃+Si, whereinthe Si is present in an amount between about 10 wt % and about 40 wt %,the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt%, and the balance being RE₂Si₂O₇; the oxide-based bond coat being theRE₂Si₂O₇+Al₂O₃+SiO2+Si, wherein the Si is present in an amount betweenabout 10 wt % and about 40 wt %, the SiO₂ is present in an amountbetween about 10 wt % and about 30 wt %, the Al₂O₃ is present in anamount between about 0.1 wt % and about 10 wt %, and the balance beingRE₂Si₂O₇; and the oxide-based bond coat being the SiO2+Al₂O₃+Si, whereinthe Si is present in an amount between about 10 wt % and about 40 wt %,the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt%, and the balance being SiO₂.

Additional features and advantages of these methods will become apparentto those skilled in the art upon consideration of the following detaileddescription of the illustrated embodiment exemplifying the best mode ofcarrying out these methods as presently perceived.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure will be described hereafter with reference to theattached drawing which is given as a non-limiting example only, inwhich:

FIG. 1 is a cross-sectional diagram of a ceramic matrix compositematerial with an oxide-based bond coat deposited thereon and a columnartop coat deposited on the oxide-based bond coat.

The exemplification set out herein illustrates embodiments of themethods and such exemplification is not to be construed as limiting thescope of the methods in any manner.

DETAILED DESCRIPTION

This present disclosure is directed to methods of fabricating multilayerenvironmental barrier coatings (EBCs) to suit the characteristics ofcertain materials such as Silicon-containing ceramics including ceramicmatrix composites (CMCs). Plasma spraying, electron beam physical vapordeposition (EB-PVD), or directed vapor deposition (DVD) are threemethods of coating CMCs.

Each deposition method has its own benefits and detriments. Oneembodiment may use plasma spraying and electron beam physical vapordeposition. Another embodiment may use plasma spraying and directedvapor deposition. By combining layers using these different methods, thebenefits of each create distinctive properties to the coatings. Forexample, an EBC may be formed by combining a plasma sprayed layer whichprovides the capability to fabricate complex chemistry coatings, with alayer formed by either DVD or EB-PVD which provides the capability tofabricate highly strain-tolerant columnar microstructures and smoothsurface finishes. The results are high performance EBCs with a multipleoxide-based bond coat having >2700 F temperature capability and a topcoat having −3000 F temperature capability. The following tableidentifies the benefits and detriments of the various coating processes.

Process Benefits Detriments Plasma Amenability to complex Inability tocoat non- Spraying coating chemistries line-of-sight areas Relativelylow Rough coating surface manufacturing cost finish Low depositionefficiency Low erosion resistance EB-PVD Smooth coating surfaceInability to coat non- (Conventional) finish line-of-sight areas Abilityto create highly Difficulty in fabricating strain-tolerant complexcoating columnar microstructures chemistries High erosion resistance Lowdeposition efficiency High manufacturing cost DVD Smooth coating surfaceDifficulty in fabricating (Enhanced finish complex coating EB-PVD)Ability to create highly chemistries strain-tolerant High manufacturingcolumnar microstructures cost, but likely Ability to coat non- line-lower than conventional of-sight areas EB-PVD High deposition efficiencyHigh erosion resistance

The benefits of plasma spraying include amenability to complex coatingchemistries and relatively low manufacturing cost, while its detrimentsinclude the inability to coat non-line-of-sight areas, rough coatingsurface finish, low deposition efficiency, and low erosion resistance.In contrast, the benefits of EB-PVD include smooth coating surfacefinish, ability to create highly strain-tolerant columnarmicrostructures and high erosion resistance. Its detriments include aninability to coat non-line-of-sight areas, difficulty in fabricatingcomplex coating chemistries, low deposition efficiency and highmanufacturing cost. The DVD (or enhanced EB-PVD) has non-line-of-sightcoating capabilities and improved deposition efficiency as compared toconventional EB-PVD.

Again, the fabrication method for each coating layer is selected byconsidering the benefits and detriments of each process in conjunctionwith the complexity of the chemistry and the function of each layer.EB-PVD or DVD may be used for the top coat of airfoils because of theirsmooth surface finish for aerodynamic performance and better erosionresistance as compared to plasma spraying. EB-PVD or DVD may also beused for layers with high coefficient of thermal expansion (CTE)mismatch with CMC. Layers having high CTE mismatch with CMC may causehigh residual stresses and therefore experience short thermal cyclinglife. CTE mismatch stresses can be significantly mitigated by creating ahighly strain tolerant columnar microstructure using the EB-PVD or DVDprocesses. Plasma spraying may be used for layers with a complexchemistry. Multiple phases react at high temperatures to formglass-containing reaction products that create strong chemical bondingfor long steam cycling life.

An illustrative embodiment provides a combination of a plasma-sprayed,complex oxide-based bond coat and either an EB-PVC or DVD-based rareearth silicate, stabilized zirconia or stabilized hafnia top coat. Thiscombination provides the EBCs with a high temperature bond coat with atemperature capability exceeding the temperature capability of currentSilicon (Si) bond coats (−2460 F), along with a highly strain-tolerantand water-vapor-resistant, low thermal conductivity top coat. The hightemperature bond coat enables the implementation of high temperatureCMCs (2700 F CMC) in gas turbines, while the highly strain-tolerant andwater-vapor-resistant, low thermal conductivity top coat increases theEBC surface temperature capability to about −3000 F.

Examples of plasma sprayed layers include oxide-based high temperaturebond coats with complex chemistry, such as mullite (3Al₂O₃-2SiO₂),mullite+Si, HfSiO₄+SiO₂+Si, HfSiO₄+Al₂O₃+SiO₂+Si, RE₂Si₂O₇+Al₂O₃+Si,RE₂Si₂O₇+Al₂O₃+SiO2+Si, SiO₂+Al₂O₃+Si, (where RE is selected from thegroup consisting of at least one of lutetium, ytterbium, thulium,erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium,promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, andscandium). When the oxide-based bond coat is mullite+Si—the Si ispresent in an amount between about 10 wt % and about 40 wt % and thebalance is mullite. When the oxide-based bond coat is HfSiO₄+SiO₂+Si—theSi is present in an amount between about 10 wt % and about 40 wt %, theSiO₂ is present in an amount between about 10 wt % and about 30 wt %,and the balance is HfSiO₄. When the oxide-based bond coat isHfSiO₄+SiO₂+Al₂O₃+Si—the Si is present in an amount between about 10 wt% and about 40 wt %, the SiO₂ is present in an amount between about 10wt % and about 30 wt %, the Al₂O₃ is present in an amount between about0.1 wt % and about 10 wt %, and the balance is HfSiO₄. When theoxide-based bond coat is RE₂Si₂O₇+Al₂O₃+Si—the Si is present in anamount between about 10 wt % and about 40 wt %, the Al₂O₃ is present inan amount between about 0.1 wt % and about 10 wt %, and the balance isRE₂Si₂O₇. When the oxide-based bond coat is RE₂Si₂O₇+Al₂O₃+SiO2+Si—theSi is present in an amount between about 10 wt % and about 40 wt %, theSiO₂ is present in an amount between about 10 wt % and about 30 wt %,the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt%, and the balance is RE₂Si₂O₇. Lastly, when the oxide-based bond coatis SiO2+Al₂O₃+Si—the Si is present in an amount between about 10 wt %and about 40 wt %, the Al₂O₃ is present in an amount between about 0.1wt % and about 10%, and the balance is SiO₂.

Examples of EB-PVD or DVD layers include EBC top coats of rare earthsilicate (RE₂Si₂O₇ and RE₂SiO₅), RE₂O₃-stabilized ZrO₂ andRE₂O₃—stabilized HfO₂ (where RE is selected from the group consisting ofat least one of lutetium, terbium, thulium, erbium, holmium, dysprosium,terbium, gadolinium, europium, samarium, promethium, neodymium,praseodymium, cerium, lanthanum, yttrium, and scandium). Rare earthmonosilicate (RE₂SiO₅), RE₂O₃—stabilized ZrO₂ and RE₂O₃-stabilized HfO₂,have CTEs substantially higher than CMC and therefore are desirable tobe fabricated in low modulus, strain tolerant columnar microstructure tomitigate CTE mismatch stresses.

The substrate may include any of the following: a Si-containing ceramic,such as silicon carbide (SiC), silicon nitride (Si₃N₄), a CMC having aSIC or Si₃N₄ matrix, silicon oxynitride, and silicon aluminumoxynitride; a Si-containing metal alloy, such as molybdenum-siliconalloys (e.g. MoSi₂) and niobium-silicon alloys (e.g. NbSi₂); and anoxide-oxide CMC. CMCs comprise a matrix reinforced with ceramic fibers,whiskers, platelets, and chopped or continuous fibers.

A cross-sectional diagram of a ceramic matrix composite material with anoxide-based bond coat deposited thereon, and a columnar top coatdeposited on the oxide-based bond coat is shown in FIG. 1. Anillustrative example of an EBC that combines plasma sprayed, hightemperature oxide-based bond coat 4 and either a DVD or EB-PVDprocessed, highly strain-tolerant columnar top coat 6, on a CMC or otherSi-containing ceramic 8. The choice of whether columnar top coat 6 isformed from either DVD or EB-PVD is determined by the particularbenefits one or the other imparts, as shown in the table above.

Although the present disclosure has been described with reference toparticular means, materials and embodiments, from the foregoingdescription, one skilled in the art can easily ascertain the essentialcharacteristics of the present disclosure and various changes andmodifications may be made to adapt the various uses and characteristicswithout departing from the spirit and scope of the present invention asset forth in the following claims.

What is claimed is:
 1. A method of making a multilayer environmentalbarrier coating for a ceramic matrix composite, the method comprisingthe steps of: plasma spray coating an oxide-based bond coat over top ofthe ceramic matrix composite; selecting a method of applying a columnartop coat over the oxide-based bond coat, wherein the method of applyingthe columnar top coat is selected from the group consisting of electronbeam physical vapor deposition and directed vapor deposition; anddepositing a columnar top coat over the oxide-based bond coat accordingto the selected method of applying the columnar top coat.
 2. The methodof making the multilayer environmental barrier coating of claim 1,wherein selecting the method of applying the columnar top coat isdecided by evaluating benefits and detriments of either the electronbeam physical vapor deposition and the directed vapor deposition methodsand how those benefits and detriments affect the columnar top coat whensprayed on the oxide-based bond coat.
 3. The method of making themultilayer environmental barrier coating of claim 1, wherein theoxide-based bond coat is selected from the group consisting of mullite,mullite+Si, HfSiO₄+SiO2+Si, HfSiO₄+SiO₂+Al₂O₃+Si, RE₂Si₂O₇+Al₂O₃+Si,RE₂Si₂O₇+Al₂O₃+SiO₂+Si, and SiO2+Al₂O₃+Si, wherein RE is selected fromthe group consisting of at least one of lutetium, ytterbium, thulium,erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium,promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, andscandium.
 4. The method of making the multilayer environmental barriercoating of claim 1, wherein the columnar top coat is selected from thegroup consisting of RE₂Si₂O₇ and RE₂SiO₅ (wherein RE is selected fromthe group consisting of at least one of lutetium, ytterbium, thulium,erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium,promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, andscandium), RE₂O₃-stabilized ZrO₂ (wherein RE is selected from the groupconsisting of at least one of lutetium, ytterbium, thulium, erbium,holmium, dysprosium, terbium, gadolinium, europium, samarium,promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, andscandium), and RE₂O₃-stabilized HfO₂ (wherein RE is selected from thegroup consisting of at least one of lutetium, ytterbium, thulium,erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium,promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, andscandium).
 5. The method of making the multilayer environmental barriercoating of claim 3, wherein the oxide-based bond coat is the mullite+Si;and wherein the Si is present in an amount between about 10 wt % andabout 40 wt %, with the balance is mullite.
 6. The method of making themultilayer environmental barrier coating of claim 3, wherein theoxide-based bond coat is the HfSiO₄+SiO₂+Si; and wherein the Si ispresent in an amount between about 10 wt % and about 40 wt %, the SiO₂is present in an amount between about 10 wt % and about 30 wt %, and thebalance is HfSiO₄.
 7. The method of making the multilayer environmentalbarrier coating of claim 3, wherein the oxide-based bond coat is theHfSiO₄+SiO₂+Al₂O₃+Si; and wherein the Si is present in an amount betweenabout 10 wt % and about 40 wt %, the SiO₂ is present in an amountbetween about 10 wt % and about 30 wt %, the Al₂O₃ is present in anamount between about 0.1 wt % and about 10 wt %, and the balance isHfSiO₄.
 8. The method of making the multilayer environmental barriercoating of claim 3, wherein the oxide-based bond coat is theRE₂Si₂O₇+Al₂O₃+Si; and wherein the Si is present in an amount betweenabout 10 wt % and about 40 wt %, the Al₂O₃ is present in an amountbetween about 0.1 wt % and about 10 wt %, and the balance is RE₂Si₂O₇.9. The method of making the multilayer environmental barrier coating ofclaim 3, wherein the oxide-based bond coat is theRE₂Si₂O₇+Al₂O₃+SiO₂+Si; and wherein the Si is present in an amountbetween about 10 wt % and about 40 wt %, the SiO₂ is present in anamount between about 10 wt % and about 30 wt %, the Al₂O₃ is present inan amount between about 0.1 wt % and about 10 wt %, and the balance isRE₂Si₂O₇.
 10. The method of making the multilayer environmental barriercoating of claim 3, wherein the oxide-based bond coat is theSiO2+Al₂O₃+Si; and wherein the Si is present in an amount between about10 wt % and about 40 wt %, the Al₂O₃ is present in an amount betweenabout 0.1 wt % and about 10 wt %, and the balance is SiO₂.